As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, have long cycle lifespan, and have a low self-discharge rate, are commercially available and widely used.
In addition, as recent interest in environmental problems is increasing, research into electric vehicles (EVs), hybrid electric vehicles (HEVs), and the like that can replace vehicles using fossil fuels, such as gasoline vehicles, diesel vehicles, and the like, which are one of the main causes behind air pollution, is actively conducted. As a power source of EVs, HEVs, and the like, research into lithium secondary batteries having high energy density, high discharge voltage, and high output stability is actively carried and such lithium secondary batteries are mainly used.
A lithium secondary battery has a structure in which an electrode assembly, which includes: a cathode manufactured by coating cathode active materials on a cathode current collector; an anode manufactured by coating anode active materials on an anode current collector; and a porous separator disposed between the cathode and the anode, is impregnated with a lithium salt-containing non-aqueous electrolyte.
In such an electrode structure, an electrode mixture portion contacting the current collector requires high electrical conductivity since the electrode mixture portion transfers electrons to an electrode active material distant from the current collector. Whereas, an electrode mixture portion distant from the current collector requires excellent electrolyte wetting properties to an electocyte and ionic conductivity. In addition, in the electrode mixture portion distant from the current collector, gas generated during charge-discharge processes may be emitted.
Therefore, there is a need to develop a technology that can resolve the above-described requirements.